Polydactylous Squamous Cell Carcinoma of the Nail Unit: A Structured Review of the Literature

Abstract

Squamous cell carcinoma of the nail unit (SCCNU) is a rare neoplastic condition that involves multiple digits (polydactylous SCCNU) in only 3.9% of cases. Here, we report a case of polydactylous SCCNU and perform a comprehensive review of MEDLINE and Embase to collate 44 cases of polydactylous SCCNU reported to date. Polydactylous patients were younger on average (48 to 61-63 years) and had a longer diagnostic delay (44 vs 35.1 months) compared with reported monodactylous cases. Human papillomavirus (HPV) positivity was observed in 49% of cases, and the most common serotypes noted were 16 (25.8%), 73 (16.1%), 58 (9.7%), 18 (6.5%), and 33 (6.5%). Twenty percent of the cases were in immunosuppressed individuals who had a statistically significant lower age at diagnosis (39.33 years vs 51.12 years; P = .01) and diagnostic delay (2.50 months vs 132.46 months, P = .04). Patients with HPV positivity had a lower age at diagnosis (43.74 years vs 53.29 years, P = .04). Environmental exposures noted to be associated with polydactylous disease included X-rays, paint/solvents, soluble oils, and stagnant water. This comprehensive literature review serves to characterize polydactylous SCCNU and distinguish the differences in its characteristics to improve diagnosis and clinical recognition.

Squamous Cell Carcinoma in Situ of the Nail Unit: Current Evidence and Recommendations for Patient Centered Treatment

“…Mohs micrographic surgery (MMS) or Slow Mohs surgery are effective and often preferred treatments for both SCCis and SCC of the nail unit due to its potential tissue sparing benefits and confirmation of histologically clear margins. 2,4,13 By excising thin successive layers until clearance is achieved, tissue removal is minimized, and digital function and cosmesis are more likely to be maintained. 13,14 Reported clearance rates for nSCCis following MMS range from 76% to 82%, but are largely derived from a limited number of case series that often analyze SCCis and invasive SCC conjointly.…”

“…2,4,13 By excising thin successive layers until clearance is achieved, tissue removal is minimized, and digital function and cosmesis are more likely to be maintained. 13,14 Reported clearance rates for nSCCis following MMS range from 76% to 82%, but are largely derived from a limited number of case series that often analyze SCCis and invasive SCC conjointly. 2,15,16 In comparison, reported clearance rates of SCC at other anatomic locations following MMS are 92% to 99%.…”

“…18 Mohs histologic assessment of the nail fold is complicated by the three dimensional topography and potential presence of multiple epithelial surfaces (nail fold, eponychium, and matrix) in a single MMS specimen. 7,13 Biopsy specimens of malignancies may also be easily transected in this location. Therefore, it may be difficult to determine whether deeply extending rete ridges were inappropriately transected, or if the tumor is truly invasive.…”

“…15,19 Additionally, the principles of tissue preservation and improved cosmesis may not be considered as relevant on the nail unit as nail bisection, permanent nail narrowing, or complete nail resection with subsequent flap reconstruction may still be required (Figures 1 and 2). 7,10,13 MMS of the nail unit should therefore only be performed by proficient surgeons who are confident with the complex anatomy and histologic analysis. 4 Furthermore, routine MMS for nSCCis is time consuming and requires additional surgical personnel and equipment.…”

“…48 Indeed, without at least partial nail plate avulsion, the application of topical therapy is limited to periungual lesions due to inadequate subungual penetration and access to proximal and lateral nail folds. 13,49 Additionally, the success of topical therapy is highly reliant on patient compliance. For these reasons, topical monotherapy for nail unit SCCis is indicated only in very limited circumstances.…”